The present invention relates to a belt for a belt drive device, and more particularly to a belt for a continuously variable belt-drive transmission for a motor vehicle.
A known continuously variable belt-drive transmission comprises an endless belt running over a drive pulley and a driven pulley. Each pulley comprises a movable conical disc which is axially moved by a fluid operated servo device so as to vary the running diameter of the belt on the pulleys in dependency on driving conditions.
The belt comprises a pair of endless carriers and a plurality of metal elements adjacently arranged on the endless carriers, engaging opposed slits of each element with the carriers. Each carrier comprises a plurality of laminated metal strips.
The carriers are repeatedly bent and straightened as they pass around the pulleys and the straight running sides, so that stress is produced in the carriers. If the stress exceeds a fatigue limit, the belt may break down by repeated stress. Thus, the service life of the belt becomes short. Japanese Patent Laid Open No. 5342172 discloses an endless metal carrier which is preliminarily bent to provide a residual stress (internal stress) in the carrier so that a maximum stress which is produced in the carrier during the operation may be below the fatigue limit. Accordingly, strength against repeated bending and straightening is improved.
However, the residual stress given in the carriers is not always content. Accordingly, the maximum stress dependent on the residual stress may exceed the fatigue limit. Namely, the strength of the belt can not be sufficiently improved.